The computer generated "'thopters" have fans on the back wings to make them fly. The actual close-up models are missing these fans.
When Stilgar is given the water from Jamis' body, he is handed it in a very small vessel and seems to require little effort to hold it. This is quite far-fetched, since he was given "33 litres," or 72 pounds in weight, which would require a much larger vessel to hold and a great deal more physical strength to carry than he seems to be exerting.